Hexagonal zirconium phosphate nanoparticles as an efficient and recyclable catalyst for selective solvent-free alkylation of phenol with cyclohexanol

• The catalyst has strong acid sites, high surface area and stability.
• 92% conversion of phenol with 88% selectivity toward 4-cyclohexylphenol were achieved.
• The results showed that cyclohexanol is a better alkylating agent than cyclohexene.
• The catalyst was regenerated easily and reused five times without loss of activity.

A facile synthesis of hexagonal α-zirconium phosphate (ZP) nanoparticles as an effective, eco-friendly and recyclable solid acid catalyst was studied. Polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA) were used as the organic matrix which were the dispersing agents and acted as a template for the nanoparticles. It seems H-bonds between ZP and PVA or PVP along polymer chains lead to a better dispersion of in situ formed ZP. Pure ZP nanoparticles with hexagonal shape were obtained after calcination of PVA/ZP or PVP/ZP. The catalysts were characterized by several physico-chemical techniques such as BET, ICP-OES, XRD, FT-IR, SEM and TEM. The TPD-NH3 analysis suggests the presence of a reasonable amount of Brønsted acid sites. The acidic properties were studied in the alkylation of phenol with cyclohexanol under solvent-free conditions which produced 2-cyclohexylphenol (2-CP), 4-cyclohexylphenol (4-CP) and 2,4-dicyclohexylphenol (2,4-DCP). This alkylation reaction was also performed over P2O5/Al2O3, P2O5/SiO2, α-ZrP (prepared in the absence of the polymers) and various ionic liquids using cyclohexanol and cyclohexene as the alkylating agents. When the hexagonal ZP nanoparticles were used as the catalyst, under optimized reaction conditions, excellent conversion of phenol and selectivity toward 4-CP were obtained. The catalyst was recovered easily from the reaction mixture, regenerated and reused at least four times without significant loss in its catalytic activity.

Figure optionsDownload high-quality image (141 K)Download as PowerPoint slide